Constant‐rate Rainfall Infiltration: Field Experiments

Abstract Measurements of water content profiles developed under constant‐rate rainfall from a simulator were reported for two field locations. The observed field profiles prior to ponding agreed with those predicted by the theory of constant‐flux infiltration. The predictions are based on field measurements of sorptivity and saturated hydraulic conductivity. Soil water diffusivity was scaled from sorptivity and wet front advance measurements taken with a simple device that gives the diffusivity of the soil matrix (i.e., the soil minus macropores > 0.75 mm diam), by supplying water to the soil surface at a slight suction. This is appropriate to nonponding flux infiltration since the soil is unsaturated. The physical properties of the matrix are shown to give the time to incipient ponding. Following saturation there may be preferential flow into the macropores so the time to initiation of runoff will lag behind the time to incipient ponding.